During use a tire is worn in the tread area which is a part of a tire that normally has a groove pattern which is in contact with the road. The tread is specifically designed to provide traction for stopping, starting, cornering and provide long lasting wear.
Wear of a tire take place over the time it is used due to friction forces working between the tire and a road surface. The friction force will also result in wear on the road surface. In the winter time, when studded tires are often used, the road surface will be especially exposed to wearing due to studs tearing up the road surface.
Worn tires will result in increased breaking distance. This is especially the case in wet weather. Without sufficient tread in a tire, aquaplaning may occur when a layer of water builds between the tire and the road surface, thus leading to a loss of traction that prevents the vehicle from responding to control inputs. This may have severe consequences.
Tires should be removed from service and replaced when they reach a certain tread depth, which is the distance from the tread surface to the bottom of the main grooves.
If worn tires are not replaced in time accidents are more likely to happen due to skidding on bald or nearly bald tires. Also, excessively worn tires are more susceptible to damage from road hazards.
Prior known methods for determining wear on a tire are visual inspection, estimation based on time used etc.
A combination of estimating the time a tire is used and visual inspection is the most common way of checking if a tire should be replaced.
When performing a visual inspection, the tread depth is measured and the tire is inspected for scratches etc.
Some tires have tread wear indicators that are located at the base of the main grooves and that are equally spaced around the tire. Built-in tread wear indicators look like narrow strips of smooth rubber across the tread that will appear on the tire when a certain point of wear is reached.
It is well known that tires are not frequently inspected and that accidents occur due to poor quality of tires.
In addition to manual inspection, there are devices for automatically detecting the wear state of a tire. Known devices for indicating wear of a tire are complex and expensive and typically comprise devices arranged in the wheel between the tire and the rim. They normally require powered electronics with sufficient power to transmit the state of the tire wear. Powering by using cables is not a good option due to rotation of the wheel. The same applies to the use of batteries since these will require inspection and maintenance since the voltage will drop over time.
EP-2368724 A1 describes a tire wear detection device comprising a piezoelectric element and a transmitter that are included in the rim of a tire. Signals from the wear detector are combined with signals from a pressure sensor unit indicating internal air pressure of the tire. The pressure sensor is arranged in the wheel. The signals from the piezoelectric element and the pressure sensor are received in a receiver unit arranged on a vehicle body.
JP-3875349 B2 describes a transmitter in a vehicle transmitting a signal to a passive transponder, typically an antenna, in the tread of a tire. When the tire is worn, the transponder is destroyed, i.e. worn off, and a response signal is not sent back. This solution does not require powered electronics in the wheel, but does require a transceiver installed in the vehicle.
Known solutions for automatically detecting wear of a tire are based on complex devices installed in the wheel and/or in the vehicle the wheel in mounted to.
There is a need for a simple and inexpensive way of automatically detecting and indicating tire wear and also the degree of wear independent of any transmitter or receiver installed in the vehicle the wheel is mounted to. It is also a need for a self-powered solution for indicating tire wear and allowing a tire to be used over several years without having to check the state of batteries powering a transmitter.
In it simplest embodiment, the present invention is based on a device detecting moisture for indicating wear of a tire.
In one embodiment the solution is totally independent by a self-powered and self-driven communication solution based on a catalytic electrode accumulator which is located below the wear surface in the tread area of a tire. When the tire has been worn to a certain degree, water will at some point penetrate and activate the accumulator that will start generating power to a transmitter, thus indicating that the tire has been worn to a certain degree.
The detecting device can be inactive in several years without any degrading of the functionality.